Electrolytic anticompromise process

ABSTRACT

Microelectronic devices and circuits, such as are found in semiconductor and hybrid microelectronics, are rendered unrecognizable and are destructed by means of an electrochemical reaction comprising an electrochemical or chemical etching and/or de-plating process.

United States Patent Rust et al. Nov. 27, 1973 [5 ELECTROLYTIC ANTICOMPROMISE 2,884,313 4/1959 Browne 204/146 PROCESS 2,758,074 8/1956 Black et al 204/146 3,409,523 11/1968 Garbarini 204/143 R 1 Inventors: J Rust, Malibu; y 2,722,511 11/1955 Butler et a1. 204/143 R Smolker, Los Angeles, both of Calif. 2,695,351 11/1954 Beck 204/143 R [73] Assignee: Hughes Aircraft Company, Culver FOREIGN PATENTS 0R APPLICATIONS y, Calif- 1,284,532 1/1962 France 204/143 [22] Fded' June 1970 Primary Examiner-.lohn H. Mack PP 51,312 Assistant Examiner-R. L. Andrews Attorney-James K. Haskell and Lewis B. Sternfels [52] U.S. Cl. 204/146 51 1111.01. B0lk 3/00 [57] ABSTRACT [58] Field of Search 204/143 R, 146 Microelectronic devices and circuits, Such as are found in semiconductor and hybrid microelectronics, 5 References Ci are rendered unrecognizable and are destructed by UNITED STATES PATENTS means of an electrochemical reaction comprising an electrochemical or chemical etching and/or de-plating 3,476,660 11/1969 Selwa 204/228 process. 3,346,477 10/1967 Wolfer 2,944,926 7/1960 Gaiser 204/146 5 Claims, 6 Drawing Figures ELECTROLYTIC ANTICOMPROMISE PROCESS The present invention relates to a process and associated apparatus which provides a means for destroying microcircuits or otherwise rendering unrecognizable details of specific circuit patterns and details of circuit device manufacture by means of an electrolytic etching and/or deplating process.

Military electronic equipment such as radars, computers, and communications equipment as well as similar and other commercial apparatus, utilizing electronic devices and circuits which contain classified or trade secret information or'technology as to their de-' sign, are protectiable insofar as non-friendly persons or competitors cannot obtain such information or technology. The'products value is seriously degraded if enemy personnel or competitors are able to obtain a sufficient amount of classified or trade secret information concerning the device parameters and modes of operation to enable the enemy personnel or competitors to develop effective countermeasures or to produce competing products. Such information is generally obtained when the item is stolen, lost in deployment, captured, or purchased on the open market.

In order to prevent such information from falling into the enemys or a competitor's hands, several approaches have been taken among which are the use of an explosive to shatter the device into many pieces and the use of microelectronic anticompromise circuits wherein a destruct mechanism destroys a thin film circuit pattern or a logic network. The first approach does not adequately destroy very small electronic circuits when placed in either hybrid microcircuits, LSI circuits, or MSI circuits whose dimensions are of only a few square inches because of its inability to render unrecognizable microcircuits of such small dimensions even after the microcircuit has been shattered into many small pieces. Regarding consumer items, such an explosive is a safety hazard and, therefore, impractical. The microelectronic technology approach is much less hazardous and hsa the ability to completely destroy miniscule critical parts without destroying neighboring parts. Furthermore, such an approach enables repair or replacement of inadvertently destroyed microcircuits. It is also possible to obtain destruction of only selected devices such as resistors, capacitors, inductors, diodes, and transistors. Consequently, the microelectronic technology approach is generally preferred.

One such approach utilizes a thermal-chemical reation in which microcircuit elements are destroyed by heat. This method is limited by the temperature rise which is possible to be brought to the elements of the microcircuit. For example, many microelectronic devices are provided with a heat-sink for cooling purposes; also, many electronic circuits are made out of thermally conductive material which will not reach its fusion temperature under any but the most unusual circumstances. For example, the heat of fusion of silicon is approximately I,400C, which is a difficult temperature to maintain in a microelectronic package. Therefore, the thermal-chemical method is undesirable for many electronic devices. In another approach, an oxidation-reduction reaction occurs only on the surface of the devices and leaves either an oxide or metal residue which could aid in the determination of initial elreuit or chemical composition of the component. Therefore, complete destruction is not obtainable.

The present invention avoids these and other problems by utilization of an electrolytic reaction by etching and/or electrochemical de-plating which does not depend upon temperature melting or fusing efi'ects for destruction of the microcircuit and is not limited o'nly'to superficial destruction. Briefly, the present invention utilizes an electrolyte in solution which is in contact with or is caused to come into contact with the microcircuit or microcircuits or the circuit patterns thereof to be destructed. The electrolyte along etches'the microcircuit but, when the microcircuit is made the an- Another object of the present invention is the provision of a method for destructing microelectronic circuits and devices.

Another object is the provision of an apparatus and I I method for destructing microelectronic circuits by electrochemical and/or de-plating means;

Another object of the present invention is to provide an apparatus and method for destroying the identity of microelectronic circuits.

Other aims and objects as well as a more complete understanding of the present invention. will appear from the following explanation of exemplary embodiments and the accompanying drawings thereof, in which:

FIG. 1 schematically illustrates a first embodiment of the present invention for packaging a destruct apparatus prior to use thereof;

FIG. 2 shows the embodiment of FIG. 1 subsequent to initiation of the destruct mechanism;

FIG. 3 depicts the first embodiment of FIGS. Land 2 after destruct has been accomplished;

FIG. 4 schematically shows a second embodiment of the present invention;

FIG. 5 depicts a third embodiment of the present invention; and

FIG. 6 shows a fourth embodiment of the present invention utilizing fuzing means to initiate the supply of electrolytic solution to a microelectronic circuit.

Accordingly, with reference to FIGS.. 1-3, a microcircuit 10 is included in or placed on a substrate 12 of silicon or germanium or the like. Device 10 and substrate 12 are packaged within an enclosure '14 into which a cathode 16 and an anode 18 are provided and sealed. A source of direct current power 20 is secured to the anode and cathode. An encapsulated salt 22 comprising an electrolyte is positioned above the microcircuit and substrate and separated therefrom by some barrier, such as a pyrotechnic metal shield 24 which is to be removed when destruct is to be initiated. A solvent 26 is placed above the salt and separated therefrom by a divider 28 in order to prevent premature formation of an electrolytic solution formed from the combination of solvent 26 and salt 22. In order to insure that the solution, when formed, will come into contact with the microcircuit and substrate, a volume expander 30 is included within enclosure 14 and separated from a solvent and salt by a barrier 32 which may be made self-removing by means such as a pyrotechnic element.

Upon removal of barriers 24, 28 and 32, the solvent and salt combine to form an electrolytic solution 34 which is thrust upon the microcircuit by expander 30, as shown in FIG. 2. Upon supply of current from source 20, acid in a nascent, highly active state forms at microcircuit and substrate 12 to cause oxidation and formation of ions therefrom which subsequently are dissolved in the solution in order to completely destroy and make unrecognizable the circuit and components therein. The result is shown in FIG. 3.

Referring now to FIG. 4, which depicts a second embodiment of the present invention, a microcircuit 40 is shown positioned upon a flat pack 42 both of which are sealed within an enclosure 44. A cathode 46 and an anode 48 which extend into and are sealed within the enclosure, are secured to a direct current source of power 50. For convenience, the separate packaging of the solvent and salt have been omitted from this figure, since they may be packaged in a manner similar to that depicted in FIG. 1. Therefore, FIG. 4 shows an electrolytic solution 52 already in contact with microcircuit and flat pack 42 as thrust thereagainst by a volume expander 54 through means of a deformable diaphragm 56. A wire 58 is shown connecting the anode to microcircuit 40 although the anode may be directly connected thereto. As described above, upon supply of power from source 50', the microcircuit is destroyed by electrochemical de-plating reactions.

Both FIGS. 1 and 4 show a volume expander, whose function is to ensure that the electrolyte will contact the microcircuit regardless of the gravity field, whether zero or not, and the physical attitude of the apparatus.

A third embodiment of the present invention is depicted in FIG. 5 wherein a circuit 60 to be destructed is positioned within an enclosure 62 sealed by means of a lid 64. A cathode 66 and an anode 68 extend within the package and are secured to a direct current source of power 70. A wire 72 connects the anode to circuit 60. In this embodiment, an electrolytic solution 74 is stored within a container 76 under pressure. Container 76 is coupled to the circuit package by a conduit 78 which is fitted within cover 64 and sealed from circuit 60 by a breakable diaphragm 80. This conduit may consist of a short path from container 76 to lid 64 allowing a pickaback configuration for container and device. Upon breaking of diaphragm 80, solution 74 flows from a container 76 into contact with circuit 60 through conduit 78 for destruct of the circuit upon supply of power from source 70.

Still another embodiment is shown in FIG. 6 for destruction of a circuit 90, which is contained within an enclosure 92 having a lid 94. In a manner similarly described above, a cathode 96 and an anode 98 connected to a source of power 100 extend within the FIG. 6 package. A wire 102 connects the anode with the circuit. In this embodiment, an electrolytic solution 104 such as an acid for etching or de-plating is contained within an ampoule 106 and placed atop lid 94. A squib cap 108 is placed around the ampoule and enclosed electrolytic solution and sealed to lid 94. A shaped charge 110 contained within a portion 110 of cap 108 is connected to an ignition source 112 and is disposed above squib 108 which is provided with a specific configuration 114 in order to provide a shaped charge. Upon energization of ignition source 112, the shaped charge explodes and punctures both ampoule 106 and lid 94 to force the electrolytic solution into contact with circuit 90. Electrochemical de-plating of the circuit occurs when current is supplied from source 100.

As stated above, the electrolytic process herein described proceeds by means of the dissolution of the microcircuit in electrolyte solutions. This process consists of the oxidation of the microcircuit, such as a silicon semiconductor, from a low oxidation state to some higher state which is soluble in the electrolytic solution. This oxidation is coupled with the reduction of species in the system. In the dissolution of a silicon semiconductor in electrolytic solution, the metal is oxidized to ions. Oxidation of metal and reduction of electrolyte occur at corresponding anodes and cathodes. At steady state, the rate of anodic and cathodic reaction is equal to the overall dissolution rate. The oxidation and reduction rates are proportional to the current flow through the anode-cathode circuit.

The preferred electrolytic etchant means for attacking silicon, silicon nitride and silicon dioxide are hydrofluoric acid and mixtures of hydrofluoric acid with nitric acid. These etchants are modified with acetic acid, phosphoric acid, ammonium fluoride, etc., to achieve enhanced results for good chemical reactions, for chemical milling and etching.

In order to obtain rapid and complete eradication of dopants, dopant patterns and interconnections in a microcircuit, it is preferred to utilize salts which will give the desired acid or combination of acids at the anode surface of the microcircuit. Such salts include sodium fluoride, potassium fluoride, ammonium fluoride, lithium fluoride, the combination of potassium fluoride and potassium phosphate, lithium fluoride combined with lithium nitrate, sodium fluoride combined with sodium nitrate, potassium fluoride combined with potassium nitrate, lithium fluoride combined with lithium phosphate, sodium fluoride combined with sodium phosphate, lithium phosphate, lithium orthophosphate, etc. Because the effect of electrolytic etching processes is generally different and more active than chemical etching processes, mixed electrolytes are able to enhance activity. Therefore, sodium chlorate, potassium chlorate, etc., may be substituted for the nitrates, sodium persulphate, ammonium persulphate, etc., in conjunction with the fluoride. Added salts may be provided such as sodium acetate, sodium phosphate, and the like.

The electrolytic processes separate the ions in the electrolyte which, when in aqueous solution. form an acid at the anode and an alkali at the cathode. In order to prevent mixing and rapid neutralization, it is desirable to slow the diffusion by making the electrolyte viscous with polymeric additives, such as hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrollidone, and deacetyla ted chitin salt, and/or to surround the cathode with a porous structure such as a porous ceramic shell or a regenerated cellulose membrane, so as to confine the alkali released at the cathode. Although the invention has been described with reference to particular embodiments thereof, it should be realized that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An anticompromise method for destructing' the identity and usefulness of otherwise operative portions of a microelectronic device having destruct means packaged therewith in isolation from the portions comprising the steps of placing the destruct means in contactwith the portions and electrolytically removing and applying electrical power to a cathode and the device through the electrolyte to create acid at the anode in a nascent, highly active state.

3. A method as in claim 2 further comprising the step destroying in a non-selective, uncontrolled manner the 5 of utilizing a means at the cathode for confining alkali identity of at least the portions of the device whereby identification and recognition of at least the portions is frustrated.

2. A method as in claim 1 wherein said step includes the steps of utilizing an electrolyte contactable with the device,

utilizing the device as an anode, and

produced at the cathode in the neighborhood of the cathode.

4. A method as in claim 2 further comprising the step of inhibiting neutralization of the electrolyte.

5. A method as in claim 1 wherein said step comprises the step of etching the device. 

2. A method as in claim 1 wherein said step includes the steps of utilizing an electrolyte contactable with the device, utilizing the device as an anode, and applying electrical power to a cathode and the device through the electrolyte to create acid at the anode in a nascent, highly active state.
 3. A method as in claim 2 further comprising the step of utilizing a means at the cathode for confining alkali produced at the cathode in the neighborhood of the cathode.
 4. A method as in claim 2 further comprising the step of inhibiting neutralization of the electrolyte.
 5. A method as in claim 1 wherein said step comprises the step of etching the device. 